With today's portable communication products becoming smaller and more compact, the designs for these products, from both an electrical and mechanical perspective, are moving towards miniaturization. The miniaturization of both electrical and mechanical components to accommodate limited space constraints has lead to an increase in issues relating to radio performance. One such issue is the occurrence of microphonics associated with voltage controlled oscillator (VCO) circuits.
Voltage controlled oscillator circuits provide the operating frequencies with which communications products transmit or receive signals. In portable radio applications, a voltage controlled oscillator typically consists of a module formed from a substrate upon which a tank circuit including a resonator is provided. The noise performance specifications associated with the VCO module are critical to the performance of the radio. A VCO module is typically shielded with a metalized can to isolate the tank circuit and maintain the stability of the frequency within the radio. Because of space restrictions, however, the shield may violate the height required to minimize field perturbations within the VCO module. Any disturbances in the tightly coupled fields of the VCO module can degrade the noise performance of the VCO and thus the radio.
Microphonic problems in radio products are associated with both mechanical and electrical limitations imposed by product size, manufacturing processes, and packaging capabilities. In the case of the VCO module, a tightly constrained metalized can tends to behave as a membrane, coupling acoustical energy into mechanical vibrations which in turn modulate the fields of the oscillator. This in turn can cause low frequency deviations to be channeled to the speaker in the form of unwanted audio signals. Depending on the severity of the vibrations, a closed loop can be formed where the radio exhibits a "howling" noise, a term commonly used for describing microphonics.
Accordingly, there is a need for an improved voltage controlled oscillator assembly which minimizes microphonics in radio communications products.